1. Field of the Invention
The present invention relates to an ink cartridge and to a method of producing the ink cartridge.
2. Description of the Related Art
Ink cartridges for supplying ink to recording devices are broadly used. One type has a case that holds a porous member impregnated with ink. Another type includes a flexible bag filled with ink. Japanese Patent-Application Publication No. 58-53473, Japanese Patent Publication No. 3-505999, and U.S. Pat. No. 4,509,062 each disclose an ink cartridge including a case with one side open. A flexible film is attached to cover the open side of the case. Ink is accommodated in between the case and the film.
It is desirable that an ink cartridge enable an ink jet head connected to a ink cartridge to stably eject ink until almost all of the ink in the ink cartridge is gone.
Conventional ink cartridges enable an ink jet head to stably eject ink while a sufficient amount of ink remains in the ink cartridge. This is because pressure for supplying the ink from the ink cartridge to the ink jet head can be maintain at a desired level while ink fills the ink cartridge. However, when the amount of ink in the ink cartridge drops below a certain level, the ink supply pressure changes so that stable ink supply cannot be continued. Therefore, ink in the ink cartridge cannot be used up completely.